There are a number of U.S. patents that disclose electronic apparatus for printing indicia on labels, some of which are restricted to hand held units and others that disclose tabletop units. The patents known to the applicants at the time of filing this application for patent are as follows. There are a large number of patents assigned to Monarch Marking Systems, Inc., all of which are restricted to hand held labeling machines: U.S. Pat. Nos. 4,264,396, Stewart; 4,407,692*, Torbeck; 4,473,426*, Goodwin et al.; 4,477,305*, Hamisch, et al; 4,479,843*, Newhard et al.; 4,488,671*, Hamisch; 4,490,206*, Makley; 4,497,682*, Hamisch; 4,498,947*, Hamisch et al; 4,511,422*, Hamisch et al.; 4,544,434*, Mistyurik; 4,556,442*, Torbeck; 4,561,926*, Hamisch et al.; 4,584,047*, Vanderpool et al.; 4,584,048*, Hamisch et al.; and 4,680,078, Vanderpool et al. Tabletop units for this general purpose, some of which are portable, are described in U.S. Pat. Nos. 4,440,248, Teraoka; 4,501,224, Shibayama; 4,630,538, Cushing; and 4,655,129, Wirth et al., assigned to the assignee of this application for patent, which relates to a marker sleeve printing apparatus developed for use with a communication terminal such as a computer. Equipment of this type that is or has been sold commercially for printing labels is represented by Monarch's Pathfinder labeler, the E-Z-Coder.RTM. printer sold by Thomas & Betts Corporation, and the Bradywriter.RTM. and Bradywriter II.RTM. industrial printers sold by the assignee of this application for patent.
The electronic machines for printing labels of this type all include the same general combination of elements, a printhead, means for feeding a web of stock to be printed past the printhead, a microprocessor, a read only memory programmed with appropriate instructions, a random access memory, a keyboard with letter, number and function keys for the entry of alphanumeric information and instructions concerning the indicia to be printed, and a visual display such as an LED or LCD unit to assist the operator in using the machine. This type of equipment is preferred by many users concerned with marking electrical wires, electrical devices such as EPROM's, IC's and other components, and various types of articles with specific identifying indicia such as a serial number or code because it allows the user to generate the required printed markers at or near the job site as needed instead of utilizing preprinted marker devices.
The present invention is concerned with a machine of this general type that includes a novel arrangement of printhead and web sensor elements to facilitate accurate registration of a marker device and the printing to be applied thereto. One of the systems for accomplishing this function as shown in the prior art represented by the above patents and commercial devices involves a tractor feed system in which the machine has a feed wheel with teeth or a sprocket that engages holes, cuts or other apertures formed in the web of labels that is to be printed. This type of system for obtaining registration between labels and a printhead is disclosed in the nine patents listed above that are marked with an asterisk and employed in the Bradywriter and Bradywriter II machines. U.S. Pat. No. 4,680,078 describes what appears to be a variation of the tractor feed that utilizes a slotted timing disk and a mating web feed roller. The disk is coded with small slots for each dot line of print and large slots for the beginning of the label. The timing disk senses the position of the web feed roller, not the web to be printed, and it appears that the feed roller must be of the type that engages apertures or other cuts in the web such as with a tractor transport in order for the device to operate properly.
Other of the listed prior art discloses the use of photoelectric sensors in this type of equipment. Thus, the electronic labeler of U.S. Pat. No. 4,264,396 includes an optical sensor spaced from and located upstream of the printhead; the sensor is to detect an ink strip or other mark printed on the web and registered with each individual label. U.S. Pat. No. 4,440,248 discloses a bar code printing apparatus that also includes a photoelectric sensor spaced from and upstream of a printhead that is said to function as a label detector to control web advancement, but details of its operation are not disclosed in the patent. The system of U.S. Pat. No. 4,501,224 has a photosensor spaced from and upstream of a printhead that detects an aperture formed in the web of stock being printed and generates an output signal that is used for timing of the printing and cutting operations. The optical sensing systems disclosed in these latter patents have two features in common: the optical sensor is a stationary element and the sensor is spaced from or separate from the printhead element of the machine.